This "Does It Work" test sheds light on flashlights that promise to last forever. They're no-battery flashlights, also called magnetic "shake lights".

There are a number of different brands and all work on the same premise: when you shake the flashlight, a movable magnet inside passes through a coil of wire and creates electricity.

So much for the science: how well does it work?

Our "Does It Work?" volunteer for this test is Kathleen Whitmore. We tested the flashlight in a storeroom at her office.

First off, we read the instructions: "Hold the unit parallel to the ground and shake it with moderate force about 2 or 3 times per second."

The longer you shake, the longer the light lasts. After shaking the flashlight for a couple of minutes, we turned out the lights and turned on the flashlight. The light has a bluish tint and projects a fairly decent beam to the wall across the room.

Others shake lights have a greenish tent. When the light starts to dim, just give it a shake.

We had enough light to continue reading the instructions, which urge caution: the strong magnetic field can cause damage.

"You cannot have a pacemaker on. No cassette tapes. No computer disks, no video tapes, credit cards, televisions, " Kathleen says.

In order to prevent damage, the magnetic flashlight must be at least a foot away from anything sensitive to magnets.

The particular model we tested, called Forever Light, cost just under $22.

"You could spend $20 on batteries in a year," Kathleen pointed out.

But can the light last for long periods of time? According to the instructions, a 10 minute shake provides 4 hours of bright light. Kathleen agreed to keep the flashlight and try it out at home.

I checked back one week later.

"Every hour I'd walk over to it and the light was dimmed quite a bit," Kathleen explained. "But I'd turn it off, shake it for 2 minutes, put it back in the corner, and it'd be just as bright as ever."

"I think it's very good for an emergency," she added. But she points out you have to shake it a lot to keep the light going. And the light is "adequate" not consistently great. But it works.

"I don't think it would work for elderly people because you can't have it around pace makers and it's heavy to shake." said Kathleen. "But other than that... it worked perfect!"

Kathleen's recommendation is to have it only for your disaster kit. She says she would not use one for everyday household use because of all the shaking required, the potential magnetic damage to electronics, and because dropping them can damage the diodes that make the light.

You can find them at hardware stores and online under a lot of different names. The quality varies and prices run from between $15 and $60.

For More Information:

Other consumer reviews:

epinions.com
epinions.com (second story)
www.stamfordadvocate.com
www.flashlightreviews.com.